Critical phase alkylation process

ABSTRACT

A process for the production of ethylbenzene by the ethylation of benzene in the critical phase over a molecular sieve aromatic alkylation catalyst comprising cerium-promoted zeolite beta. An aromatic feedstock having a benzene content of at least 90 wt. % is supplied into a reaction zone and into contact with the cerium-promoted zeolite beta having a silica/alumina mole ratio within the range of 50-150 and a cerium-aluminum ratio of 0.5-1.5. Ethylene is supplied to the alkylation reaction zone in an amount to provide a benzene/ethylene mole ratio of 1-15. The reaction zone is operated at temperature and pressure conditions in which benzene is in the super critical phase to cause ethylation of the benzene in the presence of the cerium zeolite beta alkylation catalyst. An alkylation product is produced containing ethylbenzene as a primary product with the attendant production of heavier alkylated by-products of no more than 60 wt. % of the ethylbenzene. The critical phase alkylation reaction may be followed by the transalkylation of a polyalkylated aromatic component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of parent application, Ser.No. 10/268,390, filed Oct. 4, 2002, now issued as U.S. Pat. No.6,933,418. This application was filed during the pendency of thatapplication and claims priority thereto.

FIELD OF THE INVENTION

This invention relates to the production of ethylbenzene and moreparticularly to the ethylation of benzene over a cerium-promoted betaalkylation catalyst under the conditions in which the benzene is in thesupercritical phase.

BACKGROUND OF THE INVENTION

The alkylation of benzene with ethylene over a molecular sieve catalystis a well-known procedure for the production of ethylbenzene. Typically,the alkylation reaction is carried out in a multistage reactor involvingthe interstage injection of ethylene and benzene to produce an outputfrom the reactor that involves a mixture of monoalkyl andpolyalkylbenzene. The principal monoalkylbenzene is, of course, thedesired ethylbenzene product. Polyalkylbenzenes include diethylbenzene,triethylbenzene, and xylenes.

In many cases, it is desirable to operate the alkylation reactor inconjunction with the operation of a transalkylation reactor in order toproduce additional ethylbenzene through the transalkylation reaction ofpolyethylbenzene with benzene. The alkylation reactor can be connectedto the transalkylation reactor in a flow scheme involving one or moreintermediate separation stages for the recovery of ethylene,ethylbenzene, and polyethylbenzene.

Transalkylation may also occur in the initial alkylation reactor. Inthis respect, the injection of ethylene and benzene between stages inthe alkylation reactor not only results in additional ethylbenzeneproduction but also promotes transalkylation within the alkylationreactor in which benzene and diethylbenzene react through adisproportionation reaction to produce ethylbenzene.

Various phase conditions may be employed in the alkylation andtransalkylation reactors. Typically, the transalkylation reactor will beoperated under liquid phase conditions, i.e., conditions in which thebenzene and polyethylbenzene are in the liquid phase, and the alkylationreactor is operated under gas phase conditions, i.e., pressure andtemperature conditions in which the benzene is in the gas phase.However, liquid phase conditions can be used where it is desired tominimize the yield of undesirable by-products from the alkylationreactor.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a processfor the production of ethylbenzene by the ethylation of benzene in thecritical phase over a molecular sieve aromatic alkylation catalystcomprising cerium-promoted zeolite beta. In one aspect of the invention,an aromatic feedstock having a benzene content of at least 90 wt. % issupplied into a reaction zone and into contact with the cerium-promotedzeolite beta. Preferably, the zeolite beta has a silica/alumina moleratio within the range of 20-500 and more, preferably within the rangeof 50-150. Ethylene is supplied to the alkylation reaction zone in anamount to provide a benzene/ethylene mole ratio of 1-15. The reactionzone is operated at temperature and pressure conditions in which benzeneis in the super critical phase to cause ethylation of the benzene in thepresence of the zeolite beta alkylation catalyst. An alkylation productis produced containing ethylbenzene as a primary product with theattendant production of heavier alkylated by-products of no more than 60wt. % of the ethylbenzene. The alkylation product is recovered from thereaction zone for further use or processing. Preferably, the alkylationreaction zone is operated under temperature and pressure conditionsproviding a composite by-product yield of propyl benzene and butylbenzene relative to ethylbenzene, which is no more than one-half of thecorresponding yield by-product for zeolite beta promoted with lanthanum.

In a further aspect of the invention, there is provided a process forthe production of ethylbenzene in a critical phase alkylation reactionzone followed by the transalkylation of a polyalkylated aromaticcomponent. In this aspect of the invention, there is provided analkylation reaction zone containing cerium-promoted beta aromaticalkylation catalyst. A feedstock containing benzene in an amount of atleast 95 wt. % of the aromatic content of the feedstock as a majorcomponent and ethylene as a minor component is supplied to thealkylation reaction zone. The alkylation reaction zone is operated attemperature and pressure conditions at which benzene is in the supercritical phase to cause ethylation of the benzene in the presence of thecerium-promoted zeolite beta and to produce an alkylation productcomprising a mixture of benzene, ethylbenzene, and polyalkylatedaromatics, including diethylbenzene. The alkylation product is recoveredfrom the alkylation reaction zone and supplied to a separation andrecovery zone. In the recovery zone, ethylbenzene is separated andrecovered from the product as well as the separation of a polyalkylatedcomponent including diethylbenzene. At least a portion of thepolyalkylated aromatic component, including diethylbenzene, is suppliedto a transalkylation reaction zone containing a molecular sievetransalkylation catalyst. Benzene is also supplied to thetransalkylation reaction zone, and the transalkylation reaction zone isoperated under temperature and pressure conditions to causedisproportionation of the polyalkylated aromatic fraction to produce adisproportionation product having a reduced diethylbenzene content andan enhanced ethylbenzene content. Preferably, the transalkylationreaction zone contains a zeolite Y catalyst and is operated underconditions to maintain the polyalkylated aromatic component in theliquid phase. Preferably, the cerium-promoted zeolite beta has asilica/alumina ratio within the range of 50-150 and a cerium/aluminumratio within the range of 0.25-5.0, preferably 0.5-1.5.

The cerium-promoted zeolite beta only gradually undergoes deactivationand as a result can be employed for prolonged periods of time beforeregeneration is necessary. In regenerating the catalyst, theregeneration procedure is initiated by injecting an inert oxygen-freegas, such as nitrogen, initially into the catalyst bed. The initialnitrogen injection step is carried out at any suitable temperature,normally about 300-310° C. and is continued until the benzene in the bedis depleted and the catalyst bed is essentially dry. Thereafter, oxygenis added to the nitrogen stream. Typically, this is accomplished bygradually adding air in increasing amounts while gradually decreasingnitrogen injection until only air is injected. The oxygen burns coke offthe catalyst, and the temperature gradually increases until an exothermis measured. When the temperature then decreases and falls off, normallyto a value near the initial temperature, e.g. 300-310° C. air injectionis terminated and hot nitrogen is then injected for a suitable period oftime to provide an incremental increase of perhaps 50-100° C. Airinjection is then reinstituted while progressively lessening nitrogeninjection, and the process is carried out until an exotherm is reachedand the temperature within the catalyst bed reaches a maximum and thendecreases to a value approximately that of the catalyst bed at thetermination of the previous air injection step. Air injection isterminated and hot nitrogen injection is reinstituted, and the procedureis reached until the temperature in the catalyst bed ultimately reachesa level of at least 500° C. preferably in excess of 510° C. Typically,the regeneration procedure is carried to its conclusion at a finalexotherm having a temperature within the range of about 525-550° C. Thecatalyst regenerated by this mode of operation exhibits a relativelygradual deactivation characteristic similar to that exhibited by theinitial fresh cerium-promoted zeolite beta.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an idealized schematic block diagram of analkylation/transalkylation process embodying the present invention.

FIG. 2 is a schematic illustration of a preferred embodiment of theinvention incorporating separate parallel-connected alkylation andtransalkylation reactors with an intermediate multi-stage recovery zonefor the separation and recycling of components.

FIG. 3 is a schematic illustration of an alkylation reactor comprising aplurality of series connected catalyst beds with the interstateinjection of feed components.

FIG. 4 is a graph illustrating the percent of bed used versus days onstream for an alkylation reaction carried out with a cerium modifiedzeolite beta.

FIG. 5 is a graph showing the percent of bed used for both a ceriummodified zeolite beta and a lanthanum modified zeolite beta.

FIG. 6 is a graph showing the percent of bed used for cerium modifiedzeolite beta employed as a fresh catalyst and as a regenerated catalyst.

FIG. 7 is a graph showing an ethyl benzene yield versus days on streamfor a cerium modified zeolite beta.

FIG. 8 is a graph illustrating by-product yield versus days on streamfor a cerium modified zeolite beta.

FIG. 9 is a graph showing comparative by-product yields for ceriummodified zeolite beta and a lanthanum modified zeolite beta.

FIG. 10 is a graph showing a heavy by-product yield for cerium modifiedzeolite beta and lanthanum modified zeolite beta.

FIG. 11 is a graph illustrating the yield of triethyl benzene versusdays of on stream for cerium modified zeolite beta and lanthanummodified zeolite beta.

DETAILED DESCRIPTION OF THE INVENTION

The present invention involves the critical phase alkylation of benzeneover a cerium-promoted zeolite beta alkylation catalyst under conditionsto control and desirably minimize the yield of by-products in thealkylation reaction zone. The feedstock supplied to the alkylationreaction zone comprises benzene and ethylene. Typically, the benzene andethylene streams will be combined to provide a benzene-ethylene mixtureinto the reaction zone. The benzene stream, which is mixed with theethylene either before or after introduction into the reaction zone,should be a relatively pure stream containing only very small amounts ofcontaminants. The benzene stream should contain at least 90 wt. %benzene. Preferably, the benzene stream will be at least 98 wt. %benzene with only trace amounts of such materials as toluene,ethylbenzene, and C₇ aliphatic compounds that cannot readily beseparated from benzene. The alkylation reaction zone is operated undersupercritical conditions, that is, pressure and temperature conditionswhich are above the critical pressure and critical temperature ofbenzene. Specifically, the temperature in the alkylation zone is at orabove 310° C. and the pressure is at or above 550 psia. Preferably, thetemperature in the alkylation reactor will be maintained at an averagevalue within the range of 320-350° C. and a pressure within the range of550-850 psia. If desired higher alkylation temperatures can be employedsince the cerium-promoted zeolite beta retains its structural integrityat temperatures of about 530-540° C. Zeolite beta which has not beenpromoted with cerium tends to lose its structural integrity as thetemperature reaches 500° C. The critical phase alkylation reaction isexothermic with a positive temperature gradient from the inlet to theoutlet of the reactor, providing a temperature increment increase ofabout 40° C.±10°.

The operation of the alkylation reaction zone in the supercriticalregion enables the alkylation zone to be operated under conditions inwhich the benzene-ethylene mole ratio can be maintained at relativelylow levels, usually somewhat lower than the benzene-ethylene mole ratioencountered when the alkylation reaction zone is operated under liquidphase conditions. In most cases, the benzene-ethylene mole ratio will bewithin the range of 1-15. Preferably, the benzene mole ratio will bemaintained during at least part of a cycle of operation at a levelwithin the lower end of this range, specifically, at a benzene-ethylenemole ratio of less than 10. A benzene-ethylene mole ratio within therange of 3-8 may be employed. Thus, operation in the supercritical phaseoffers the advantages of gas phase alkylation in which thebenzene-ethylene ratio can be kept low but without the problemsassociated with by-product formation, specifically xylene formation,often encountered in gas-phase alkylation. At the same time, operationin the super critical phase offers the advantages accruing to liquidphase alkylation in which the by-product yield is controlled to lowlevels. The pressures required for operation in the super critical phaseare not substantially greater than those required in liquid phasealkylation, and the benzene in the supercritical phase functions as asolvent to keep the zeolite beta catalyst clean and to retard cokingleading to deactivation of the catalyst.

As indicated by the experimental work described later, thecerium-promoted beta enables super critical phase alkylation to becarried out with by-products that are substantially less than thecorresponding by-products produced with super critical phase alkylationemploying lanthanum-promoted zeolite beta of similar or greater content.Thus, the alkylation reaction zone can be operated at super criticalphase temperature and pressure conditions to provide a compositeby-product yield of propylbenzene and butylbenzene which is less thanthe corresponding composite by-product yield of propylbenzene andbutylbenzene for a corresponding zeolite beta catalyst promoted withlanthanum at a lanthanum/beta atomic ratio at least as great as thecerium/aluminum atomic ratio of the cerium-promoted zeolite beta.Preferably, the alkylation reaction zone is operated at temperature andpressure conditions to provide a composite product yield ofpropylbenzene and butylbenzene which is no more than one-half of thecorresponding composite by-product yield of propylbenzene andbutylbenzene produced with the lanthanum-promoted zeolite beta.

Turning now to FIG. 1, there is illustrated a schematic block diagram ofan alkylation/transalkylation process employing the present invention.As shown in FIG. 1, a product stream comprising a mixture of ethyleneand benzene in a mole ratio of benzene to ethylene of about 1 to 15 issupplied via line 1 through a heat exchanger 2 to an alkylation reactionzone. Alkylation zone 4 preferably comprises one or more multi-stagereactors having a plurality of series-connected catalyst beds containinga cerium zeolite beta alkylation catalyst as described herein. Thealkylation zone 4 is operated at temperature and pressure conditions tomaintain the alkylation reaction in the supercritical phase, i.e. thebenzene is in the supercritical state, and at a feed rate to provide aspace velocity enhancing diethylbenzene production while retardingby-products production. Preferably, the space velocity of the benzenefeed stream will be within the range of 10-150 hrs.⁻¹ LHSV per bed.

The output from the alkylation reactor 4 is supplied via line 5 to anintermediate benzene separation zone 6 that may take the form of one ormore distillation columns. Benzene is recovered through line 8 andrecycled through line 1 to the alkylation reactor. The bottoms fractionfrom the benzene separation zone 6, which includes ethylbenzene andpolyalkylated benzenes including polyethylbenzene, is supplied via line9 to an ethylbenzene separation zone 10. The ethylbenzene separationzone may likewise comprise one or more sequentially connecteddistillation columns. The ethylbenzene is recovered through line 12 andapplied for any suitable purpose, such as in the production of vinylbenzene. The bottoms fraction from the ethylbenzene separation zone 10,which comprises polyethylbenzene, principally diethylbenzene, issupplied via line 14 to a transalkylation reactor 16. Benzene issupplied to the transalkylation reaction zone through line 18. Thetransalkylation reactor, which preferably is operated under liquid phaseconditions, contains a molecular sieve catalyst, preferably zeolite-Y,which has a somewhat larger pore size than the cerium-modified zeolitebeta used in the reaction alkylation zone. The output from thetransalkylation reaction zone is recycled via line 20 to the benzeneseparation zone 6.

Referring now to FIG. 2, there is illustrated in greater detail asuitable system incorporating a multi-stage intermediate recovery zonefor the separation and recycling of components involved in the criticalphase alkylation and transalkylation process. As shown in FIG. 2, aninput feed stream is supplied by fresh ethylene through line 31 andfresh benzene through line 32. As noted previously, the fresh benzenestream supplied via line 32 preferably is of high purity containing atleast 98 wt. %, preferably about 99 wt. %, benzene with no more than 1wt. % other components. Typically, the fresh benzene stream will containabout 99.5 wt. % benzene, less than 0.5% ethylbenzene, with only traceamounts of non-aromatics and toluene. Line 32 is provided with apreheater 34 to heat the benzene stream consisting of fresh and recycledbenzene to the desired temperature for the supercritical alkylationreaction. The feed stream is supplied through a two-way, three-positionvalve 36 and inlet line 30 to the top of one or both parallel criticalphase alkylation reactor 38 and 38A comprising a plurality of seriesconnected catalyst beds each of which contains the desired molecularsieve alkylation catalyst. The reactors are operated at an averagetemperature, preferably within the range of 300°-350° C. inlettemperature and at pressure conditions of about 650 to 800 psia, tomaintain the benzene in the critical phase. As mentioned previously,because of the high temperature structural integrity of cerium-promotedzeolite beta, the alkylation reaction zone can be operated attemperatures of up to about 500° C. and even beyond that to temperaturesof about 540° C.

In normal operation of the system depicted in FIG. 2, both reactionzones 38 and 38A may, during most of a cycle of operation, be operatedin a parallel mode of operation in which they are both in service at thesame time. In this case, valve 36 is configured so that the input streamin line 30 is roughly split in two to provide flow to both reactors inapproximately equal amounts. Periodically, one reactor can be takenoff-stream for regeneration of the catalyst. Valve 36 is then configuredso that all of the feed stream from line 30 can be supplied to reactor38 while the catalyst beds in reactor 38A are regenerated and visaversa. The regeneration procedure will be described in detail below butnormally will take place over a relatively short period of time relativeto the operation of the reactor in parallel alkylation mode. Theregeneration procedure preferably is carried out at temperaturessubstantially in excess of those normally employed in the regenerationof zeolite beta-type catalysts. When regeneration of the catalyst bedsin reactor 38A is completed, this catalyst can then be returnedon-stream, and at an appropriate point, the reactor 38 can be takenoff-stream for regeneration. This mode of operation involves operationof the individual reactors at relatively lower space velocities forprolonged periods of time with periodic relatively short periods ofoperation at enhanced, relatively higher space velocities when onereactor is taken off-stream. By way of example, during normal operationof the system with both reactors 38 and 38A on-stream, the feed streamis supplied to each reactor to provide a space velocity of about 25-45hr.⁻¹ LHSV. When reactor 38A is taken off-stream and the feed ratecontinues unabated, the space velocity for reactor 38 will approximatelydouble to 50-90 hr.⁻¹ LHSV. When the regeneration of reactor 38A iscompleted, it is placed back on-stream, and again the feed stream ratespace velocity for each reactor will decrease to 25-45 hr.⁻¹ until suchpoint as reactor 38 is taken off-stream, in which case the flow rate toreactor 38A will, of course, increase, resulting again in a transientspace velocity in reactor 38 of about 50-90 hr.⁻¹ LHSV.

A preferred reactor configuration is shown in detail in FIG. 3. Asillustrated there, the reactor 38 comprises five series connectedcatalyst beds designated as beds A, B, C, D, and E. A benzene-ethylenefeed stream is supplied to the top of the reactor and into Bed A. Anethylene feed stream is supplied via line 39 and proportionating valves39 a, 39 b and 39 c to provide for the appropriate interstage injectionof ethylene. Benzene can also be introduced between the catalyst stagesby means of secondary benzene supply lines 41 a, 41 b and 41 c,respectively. As will be recognized, the parallel reactor 38A will beconfigured with similar manifolding as shown in FIG. 3 with respect toreactor 38.

Returning to FIG. 2, the effluent stream from one or both of thealkylation reactors 38 and 38A is supplied through a two-way,three-position outlet valve 44 and outlet line 45 to a two-stage benzenerecovery zone which comprises as the first stage a prefractionationcolumn 47. Column 47 is operated to provide a light overhead fractionincluding benzene which is supplied via line 48 to the input side ofheater 34 where it is mixed with benzene in line 32 and then to thealkylation reactor input line 30. A heavier liquid fraction containingbenzene, ethylbenzene and polyethylbenzene is supplied via line 50 tothe second stage 52 of the benzene separation zone. Stages 47 and 52 maytake the form of distillation columns of any suitable type, typically,columns having from about 20-60 trays. The overhead fraction from column52 contains the remaining benzene, which is recycled via line 54 to thealkylation reactor input. Thus, lines 48 and 54 correspond to the outputline 8 of FIG. 1. The heavier bottoms fraction from column 52 issupplied via line 56 to a secondary separation zone 58 for the recoveryof ethylbenzene. The overhead fraction from column 58 comprisesrelatively pure ethylbenzene, which is supplied to storage or to anysuitable product destination by way of line 60. By way of example, theethylbenzene may be used as a feed stream to a styrene plant in whichstyrene is produced by the dehydrogenation of ethylbenzene. The bottomsfraction containing polyethylbenzenes, heavier aromatics such as cumeneand butyl benzene, and normally only a small amount of ethylbenzene issupplied through line 61 to a tertiary polyethylbenzene separation zone62. As described below, line 61 is provided with a proportioning valve63 which can be used to divert a portion of the bottoms fractiondirectly to the transalkylation reactor. The bottoms fraction of column62 comprises a residue, which can be withdrawn from the process via line64 for further use in any suitable manner. The overhead fraction fromcolumn 62 comprises a polyalkylated aromatic component containingdiethylbenzene and a smaller amount of triethylbenzene and a minoramount of ethylbenzene is supplied to an on stream transalkylationreaction zone. Similarly as described above with respect to thealkylation reactors, parallel transalkylation reactors 65 and 66 areprovided through inlet and outlet manifolding involving valves 67 and68. Both of reactors 65 and 66 can be placed on stream at the same timeso that both are in service in a parallel mode of operation.Alternatively, only one transalkylation reactor can be on-stream withthe other undergoing regeneration operation in order to burn coke offthe catalyst beds. By minimizing the amount of ethylbenzene recoveredfrom the bottom of column 58, the ethylbenzene content of thetransalkylation feed stream can be kept small in order to drive thetransalkylation reaction in the direction of ethylbenzene production.The polyethylbenzene fraction withdrawn overhead from column 62 issupplied through line 69 and mixed with benzene supplied via line 70.This mixture is then supplied to the on-line transalkylation reactor 65via line 71. Preferably, the benzene feed supplied via line 70 is ofrelatively low water content, about 0.05 wt. % or less. Preferably, thewater content is reduced to a level of about 0.02 wt. % or less and morepreferably to less than 0.01 wt. %, down to 0.002 wt. % or less. Thetransalkylation reactor is operated as described before in order tomaintain the benzene and alkylated benzenes within the transalkylationreactor in the liquid phase. Typically, the transalkylation reactor maybe operated to provide an average temperature within the transalkylationreactor of about 65°-290° C. and an average pressure of about 600 psi.The preferred catalyst employed in the transalkylation reactor iszeolite Y. The weight ratio of benzene to polyethylbenzene should be atleast 1:1 and preferably is within the range of 1:1 to 4:1.

The output from the transalkylation reactor or reactors containingbenzene, ethylbenzene, and diminished amounts of polyethylbenzene isrecovered through line 72. Typically, line 72 will be connected to theinlet lines 47 a for recycle to the prefractionation column 47 as shown.However, the effluent from the liquid-phase transalkylation reactor maybe supplied to either or both of distillation columns 47 and 52.

Returning to the operation of the separation system, in one mode ofoperation the entire bottoms fraction from the ethylbenzene separationcolumn 58 is applied to the tertiary separation column 62 with overheadfractions from this zone then applied to the transalkylation reactor.This mode of operation offers the advantage of relatively long cyclelengths of the catalyst in the transalkylation reactor betweenregeneration of the catalyst to increase the catalyst activity. Anothermode of operation of the invention achieves this advantage by supplyinga portion of the output from the ethylbenzene separation column 58through valve 63 directly to the transalkylation reactor.

As shown in FIG. 2, a portion of the bottoms fraction from the secondaryseparation zone 58 bypasses column 62 and is supplied directly to thetransalkylation reactor 65 via valve 63 and line 88. A second portion ofthe bottoms fraction from the ethylbenzene column is applied to thetertiary separation column 62 through valve 63 and line 90. The overheadfraction from column 62 is commingled with the bypass effluent in line88 and the resulting mixture is fed to the transalkylation reactor vialine 67. In this mode of operation a substantial amount of the bottomsproduct from column 58 can be sent directly to the transalkylationreactor, bypassing the polyethylbenzene column 62. Normally, the weightratio of the first portion supplied via line 88 directly to thetransalkylation reactor to the second portion supplied initially vialine 90 to the polyethylbenzene would be within the range of about 1:2to about 2:1. However, the relative amounts may vary more widely to bewithin the range of a weight ratio of the first portion to the secondportion in a ratio of about 1:3 to 3:1.

The molecular sieve catalyst employed in the critical phase alkylationreactor is a zeolite beta catalyst that can be a conventional zeolitebeta modified by the inclusion of cerium as described below. Thecerium-promoted zeolite beta catalyst will normally be formulated inextrudate pellets of a size of about ⅛-inch or less, employing a bindersuch as silica or alumina. A preferred form of binder is silica, whichresults in catalysts having somewhat enhanced deactivation andregeneration characteristics than zeolite beta formulated with aconventional alumina binder. Typical catalyst formulations may includeabout 20 wt. % binder and about 80 wt. % molecular sieve. The catalystemployed in the transalkylation reactor normally will take the form of azeolite Y catalyst, such as zeolite Y or ultra-stable zeolite Y. Variouszeolites of the Y and beta types are in themselves well known in theart. For example, zeolite Y is disclosed in U.S. Pat. No. 4,185,040 toWard, and zeolite beta is disclosed in U.S. Pat. No. 3,308,069 toWadlinger and U.S. Pat. No. 4,642,226 to Calvert et al.

The cerium-promoted zeolite beta employed in the critical phasealkylation reactor can be a zeolite beta of the type described inWadlinger or Calvert, which has been modified by the inclusion of ceriumin the crystalline framework. The cerium-promoted zeolite beta employedin the present invention can be based on a high silica/alumina ratiozeolite beta or a ZSM-12 modified zeolite beta as described in detailbelow.

Basic procedures for the preparation of zeolite beta are well known tothose skilled in the art. Such procedures are disclosed in theaforementioned U.S. Pat. No. 3,308,069 to Wadlinger et al and U.S. Pat.No. 4,642,226 to Calvert et al and European Patent Publication No.159,846 to Reuben, the disclosures of which are incorporated herein byreference. The zeolite beta can be prepared to have a low sodiumcontent, i.e. less than 0.2 wt. % expressed as Na₂O and the sodiumcontent can be further reduced to a value of about 0.02 wt. % by an ionexchange treatment.

As disclosed in the above-referenced U.S. patents to Wadlinger et al.,and Calvert et al, zeolite beta can be produced by the hydrothermaldigestion of a reaction mixture comprising silica, alumina, sodium orother alkyl metal oxide, and an organic templating agent. Typicaldigestion conditions include temperatures ranging from slightly belowthe boiling point of water at atmospheric pressure to about 170° C. atpressures equal to or greater than the vapor pressure of water at thetemperature involved. The reaction mixture is subjected to mildagitation for periods ranging from about one day to several months toachieve the desired degree of crystallization to form the zeolite beta.Unless steps are taken to minimize the alumina content, the resultingzeolite beta is normally characterized by a silica to alumina molarratio (expressed as SiO₂/Al₂O₃) of between about 20 and 50.

The zeolite beta is then subjected to ion exchange with ammonium ions atuncontrolled pH. It is preferred that an aqueous solution of aninorganic ammonium salt, e.g., ammonium nitrate, be employed as theion-exchange medium. Following the ammonium ion-exchange treatment, thezeolite beta is filtered, washed and dried, and then calcined at atemperature between about 530° C. and 580° C. for a period of two ormore hours.

Zeolite beta can be characterized by its crystal structure symmetry andby its x-ray diffraction patterns. Zeolite beta is a molecular sieve ofmedium pore size, about 5-6 angstroms, and contains 12-ring channelsystems. Zeolite beta is of tetragonal symmetry P4₁22, a=12.7, c=26.4 Å(W. M. Meier and D. H. Olson Butterworth, Atlas of Zeolite StructureTypes, Heinemann, 1992, p. 58); ZSM-12 is generally characterized bymonoclinic symmetry. The pores of zeolite beta are generally circularalong the 001 plane with a diameter of about 5.5 angstroms and areelliptical along the 100 plane with diameters of about 6.5 and 7.6angstroms. Zeolite beta is further described in Higgins et al, “Theframework topology of zeolite beta,” Zeolites, 1988, Vol. 8, November,pp. 446-452, the entire disclosure of which is incorporated herein byreference.

The cerium-promoted zeolite beta employed in carrying out the presentinvention may be based upon conventional zeolite beta, such as disclosedin the aforementioned patent to Calvert et al. For a further descriptionof procedures for producing zeolite beta useful in accordance with thepresent invention, reference is made to the aforementioned U.S. Pat. No.3,308,069 to Wadlinger, U.S. Pat. No. 4,642,226 to Calvert, and U.S.Pat. No. 5,907,073 to Ghosh and EPA Publication No. 507,761 toShamshoum, the entire disclosures of which are incorporated herein byreference.

The invention can also be carried out with a zeolite beta having ahigher silica/alumina ratio than that normally encountered. For example,as disclosed in EPA Publication No. 186,447 to Kennedy, a calcinedzeolite beta can be dealuminated by a steaming procedure in order toenhance the silica/alumina ratio of the zeolite. Thus, as disclosed inKennedy, a calcined zeolite beta having a silica/alumina ratio of 30:1was subjected to steam treatment at 650° C. and 100% steam for 24 hoursat atmospheric pressure. The result was a catalyst having asilica/alumina ratio of about 228:1, which was then subjected to an acidwashing process to produce a zeolite beta of 250:1. Various zeolitebetas, such as described above, can be subject to extraction proceduresin order to extract aluminum from the zeolite beta framework byextraction with nitric acid. Acid washing of the zeolite beta is carriedout initially to arrive at a high silica/alumina ratio zeolite beta.This is followed by ion-exchanging cerium into the zeolite framework.There should be no subsequent acid washing in order to avoid removingcerium from the zeolite.

The procedure disclosed in EP 507,761 to Shamshoum, et al forincorporation of lanthanum into zeolite beta can be employed to producethe cerium promoted zeolite beta used in the present invention. Thus,cerium nitrate may be dissolved in deionized water and then added to asuspension of zeolite beta in deionized water following the protocoldisclosed in EP 507,761 for the incorporation of lanthanum into zeolitebeta by ion exchange. Following the ion exchange procedure, the ceriumexchanged zeolite beta can then be filtered from solution washed withdeionized water and then dried at a temperature of 110° C. The powderedcerium exchanged zeolite beta can then be molded with an aluminum orsilicon binding agent followed by extrusion into pellet form.

In experimental work carried out respecting the present invention,alkylation reactor runs were carried out employing a single stagealkylation reactor. The reactor operated as a laboratory simulation ofthe single stage of a multiple stage reactor of the type illustrated inFIG. 3. In carrying out the experimental work a cerium promoted zeolitebeta having a silica alumina ratio of 150 and a cerium/aluminum atomicratio of 0.75 was employed. This catalyst was formed employing a silicabinder. Comparative experimental work was employed carrying out alanthanum promoted zeolite beta catalyst, also having a silica aluminaratio of 150 and having a lanthanum/aluminum atomic ratio of 1.0formulated with a silica binder.

The cerium promoted zeolite beta was used in the alkylation reactorthrough five (5) regenerations for a total cumulative time of in excessof 140 days. Throughout the successive runs the inlet temperature or thereactor was about 300° C.±5° C. and the temperature at the outlet of thereactor was about 350° C.±10° C. resulting in an incremental temperatureincrease across the reactor of about 40-50° C. The reactor was operatedat a inlet pressure of about 600 PSIG with a pressure gradient acrossthe reactor of only a few pounds per square inch.

The lanthanum promoted zeolite beta was employed in a test run spanningabout 55 days on line with regeneration of the catalyst at theconclusion of 20 days. The lanthanum promoted zeolite beta had a silicaalumina ratio of 150 and a lanthanum/aluminum atomic ratio of 1.0.

The results of the experimental work carried out with the cerium betacatalyst are illustrated in FIGS. 4-11. Turning initially to FIG. 4 thepercent of the bed used in the catalytic reaction is plotted on theordinate versus the total cumulative days on stream on the abscissa. Thepercent of the catalyst bed was calculated based upon the maximumtemperature sensed across the bed employing 6 temperature sensors spacedfrom the inlet to the outlet of the reactor. The percent of the bed usedwas calculated based upon the maximum temperature sensed at thetemperature sensors across the bed. In FIG. 4 Curve 101 indicates thepercent of bed used during the use of the fresh catalyst for an initialperiod of about 64 days. Curves 102, 103, 104, 105 and 106 show theresults obtained after successive regeneration of the catalysts. Curve106 indicates the results obtained for the catalyst after beingregenerated by a high temperature regeneration procedure as describedbelow in more detail with respect to FIG. 6.

FIG. 5 shows the catalyst bed used in the catalytic reaction as afunction of days on stream for the fresh cerium beta catalyst indicatedby Curve 108 corresponding to Curve 101 in FIG. 4 versus resultsobtained for lanthanum beta indicated by Curve 109. Curve 109 shows theresults for fresh catalyst (109 a), and successively regeneratedlanthanum promoted beta catalyst indicated by Curves 109 b, 109 c, 109c, 109 d and 109 e. As can be seen from a comparison of Curves 108 and109 the cerium promoted zeolite beta had a much higher stability over aprolonged period of time than exhibited by lanthanum beta over a seriesof successive regenerations.

FIG. 6 shows the percent of bed used plotted on the ordinate versus runtime and days plotted on the abscissa for the fresh catalyst and for thecatalyst after each regeneration. In each case, the days elapsed afterinitiation with a fresh catalyst, and after initiation after eachregeneration are shown. In FIG. 6 Curves 111 and 112 are linear plotsfor the fresh catalyst (Curve 111) and for the catalyst after five (5)regenerations with the last regeneration being carried out under hightemperature conditions (Curve 112). As can be seen from an examinationof the data shown in FIG. 6, after regeneration under normal temperatureconditions at maximum temperature of about 475° C. the cerium promotedzeolite beta deactivated very rapidly. However, for the catalystregenerated under the high temperature conditions in accordance with thepresent invention maximum temperature about 530° C. the catalystdeactivation rate corresponded generally to the catalyst deactivationobserved for the fresh catalyst.

FIG. 7 shows the ethyl benzene yield, EB, in terms of percent conversionplotted on the ordinate versus the total cumulative days on stream forthe cerium promoted zeolite beta. It will be recognized that the days onstream can be correlated with the regeneration data shown in FIG. 4.Thus, the fresh catalyst showed essentially a constant ethyl benzeneconversion over the 64 day run carried out with the fresh catalyst. Theanomalous results showing an ethyl benzene conversion at about 9% fordays 55, 56 and 57 correlated with an inadvertent shutdown of thereactor.

FIG. 8 shows the by-product yield, BP, relative to ethyl benzene plottedin parts per million plotted on the ordinate versus for propyl benzene,butyl benzene and heavy components for the first 130 days of the run. Ascan be seen, the butyl benzene yield was less than 1000 ppm in thepropyl benzene yield less than 500 ppm over the run time of 130 days.The heavy yield varied from about 5000 ppm to about 2000 ppm or slightlyless. As discussed below these values are substantially better than thecorresponding values observed for the lanthanum promoted zeolite beta.

The comparative results for the propyl and butyl benzenes for the ceriumpromoted beta and the lanthanum promoted beta are illustrated in FIG. 9.FIG. 9 is a plot of the designated by-products in ppm versus relative toethyl benzene plotted on the ordinate versus the days on stream on theabscissa. FIG. 10 shows corresponding data for the heavies for thecerium beta and the lanthanum beta. As can be seen from examination ofthe data in FIGS. 9 and 10 the cerium beta alkylation catalyst showedsubstantially lower by-products yields in each of the three (3)categories as was the case for the lanthanum promoted beta.Specifically, the composite by-product yield of propylbenzene andbutylbenzene produced during super critical phase alkylation over thecerium-promoted zeolite beta was less than one-half of the correspondingby-product yield of propylbenzene and butylbenzene observed for thelanthanum-promoted zeolite beta.

FIG. 11 illustrates the triethyl benzene yield (TEB) in parts permillion relative to ethyl benzene plotted on the ordinate versus thetime on stream and days plotted on the abscissa. The data for the ceriumbeta catalyst was plotted for the first 52 days of the run carried outwith the fresh catalyst. The data for the lanthanum beta zeolite showsresults for lanthanum beta after a series of regenerations. As can beseen from an examination of FIGS. 9, 10 and 11 the substantiallyimproved characteristics of the cerium promoted beta over the lanthanumpromoted beta in terms of the heavy by-product yield comes at theexpense of a moderately higher triethlybenzene production for the ceriumbeta.

Having described specific embodiments of the present invention, it willbe understood that modifications thereof may be suggested to thoseskilled in the art, and it is intended to cover all such modificationsas fall within the scope of the appended claims.

1. In a process for regenerating a deactivated cerium promoted zeolitebeta catalyst comprising: (a) injecting an inert oxygen-freeregeneration gas into a catalyst bed containing deactivated ceriumpromoted zeolite beta at an elevated temperature sufficient toessentially dry said catalyst bed; (b) progressively increasing thetemperature of said catalyst bed by incorporating oxygen into saidregeneration gas and progressively increasing the oxygen content of theregeneration gas; (c) thereafter injecting an inert oxygen-freeregeneration gas into said catalyst bed at a temperature greater thanthe temperature in paragraph (a); (d) continuing the introduction ofsaid regeneration gas containing oxygen until the temperature of thecatalyst in said catalyst bed reaches a level of at least 500° C.; and(e) thereafter cooling the cerium promoted zeolite beta in said catalystbed.
 2. The process of claim 1 wherein the incremental increase intemperature at the conclusion of subparagraph (c) is at least greater by50-100° C. than the temperature in subparagraph (a).
 3. The process ofclaim 1 wherein the regeneration procedure is carried out to provide amaximum temperature within a range of 515-550° C.
 4. The process ofclaim 1 wherein said inert oxygen free regeneration gas is introducedinto said catalyst beds through at least three cycles of operation withthe intervening injection of oxygen into said regeneration gas.
 5. Theprocess of claim 1 wherein said catalyst contains cerium in an amount toprovide a cerium/aluminum atomic ratio within a range of 0.25-5.0. 6.The process of claim 5 wherein said zeolite beta catalyst has acerium/aluminum atomic ratio within the range of 0.5-1.5.
 7. The processof claim 5 wherein said cerium-promoted zeolite beta catalyst has asilica/alumina mole ratio within a range of 50-150.
 8. The method ofclaim 1 wherein said cerium-promoted zeolite beta catalyst is formedwith a silica binder.
 9. In a process for regenerating a deactivatedcerium promoted zeolite beta catalyst comprising: (a) injecting a streamof a nitrogen regeneration gas into a catalyst bed containingdeactivated cerium promoted zeolite beta at an elevated temperaturesufficient to essentially dry said catalyst bed; (b) progressivelyincreasing the temperature of said catalyst bed by adding air into saidregeneration gas stream while progressively decreasing the amount ofnitrogen in said regeneration gas stream and progressively increasingthe amount of air in said regeneration gas stream; (c) terminating theair injected in subparagraph (b) and injecting a stream of a nitrogenregeneration gas into said catalyst bed at a temperature greater thanthe temperature in paragraph (a); (d) progressively increasing thetemperature of said catalyst bed by adding air into the regeneration gasstream of subparagraph (c) while progressively decreasing the amount ofnitrogen in said regeneration gas stream and progressively increasingthe amount of air in said regeneration gas stream; (e) terminating theair injected in subparagraph (d) and injecting a stream of a nitrogenregeneration gas into said catalyst bed at a temperature greater thanthe temperature in paragraph (c); (f) continuing the introduction ofsaid nitrogen regeneration gas stream and incorporating air into saidstream until the temperature of the catalyst in said catalyst bedreaches a level of at least 500° C.; and (g) thereafter cooling thecerium promoted zeolite beta in said catalyst bed.
 10. The process ofclaim 9 wherein the regeneration procedure is carried out to provide amaximum temperature within a range of 515-550° C.
 11. The process ofclaim 9 wherein said catalyst contains cerium in an amount to provide acerium/aluminum atomic ratio within then range of 0.25-5.0.
 12. Theprocess of claim 11 wherein said zeolite beta catalyst has acerium/aluminum atomic ratio within the range of 0.5-1.5.
 13. Theprocess of claim 9 wherein said cerium-promoted zeolite beta catalysthas a silica/alumina mole ratio within a range of 50-150.
 14. The methodof claim 9 wherein said cerium-promoted zeolite beta catalyst is formedwith a silica binder.
 15. The process of claim 9 wherein the incrementalincrease in temperature at the conclusion of subparagraph (c) is atleast greater by 50-100° C. than the temperature in subparagraph (a).